[lestercity12]

well after replacing just about everything under the hood of my jeep to try to fix this stalling, bucking problem. i have found a temporary solution. It seems the connection on the middle(white) connector that goes to the pcm has some sort of problem keeping a connection. Whenever i wiggle this connector my jeep will shut off or for that matter stay on. I have zip tied the connector almost pulling out of the pcm and that seems to be helping wonders. My jeep would buck, stall, backfire, shutoff, like many others i have been reading about. i was wondering if anybody had any other suggestions to a permanent fix. do you think its the wiring harness or the connections on the pcm? and also why would my jeep buck, stall more if its just rained or wet outside? i have spent many months and tons of money trying to fix this problem, and come to find out its something just a simple as this. one more question. why would my check engine light randomly come on and then go off when its bucking/ stalling i get codes. 12/14/42/43/55. i hook it up to a scanner and i get MAP voltage to high, and Primary Ignition Coil A. and then sometimes it passes with no codes. any help or thoughts would be great?

 

[Osboy1]

... and also why would my jeep buck, stall more if its just rained or wet outside? ...

As your connectors are loose / shorted / broken, and the dielectric grease has worn off, you can expect the connections to be sensitive to increased moisture.

There are a number of write-ups on this issue, but a good cleaning and re-lubricating of the connectors, as well as a careful inspection of the wires in the harness might provide a more lasting fix.

If you have damaged wires in your harness, they will need to be repaired or replacd. If your PCM is damaged from the shorting and voltage variations over such a long period of time, you will eventually need to replace it.

But

 

[ZeeJay1997]

Zip ties are a way of life on my Jeep.

 

[purplecty]

just remove coolant reservoir and then zip tie each one? u got a pic because maybe it will cure my surging at stops and low idle???

 

[ZeeJay1997]

Go to a hardware store or building supply. Pick up some 24 inch zip ties, dielectric grease, electrical contact cleaner. Take reservoir out. Remove connectors from PCM, clean plug and socket, let them dry. When they are dry, apply grease and reconnect.

Place zip ties vertically over the back side of the PCM and over the top of the connectors and cinch them down tight.

You can see it fairly well in this pic

 

[Canyon411]

response to coil as cause of issue ...

In my experience, coils are either good or bad. Sometimes you will get a heat-soak issue that will cause a coil to stop working until it cools off again, but intermitant stumbling/surging seems like another issue. Going to try the suggestion of contact cleaner and dielectric grease and see if that cures my stumble/surge issue as well.

 

[purplecty]

zeejay thanks for the tip. i think i saw u post this many times before and i dont know why i never tried this yet. i dont remember why u zip tied in the first plac. didnt u have a surge/stumble problem as well? anything else youve done i should pay attention to? since i see we have the exact same jeep.... i will try to get around to it this weekend and will post back...

 

[Osboy1]

Zeejay... that is the cleanest ZJ engine compartment I have ever seen.

 

[ZeeJay1997]

zeejay thanks for the tip. i think i saw u post this many times before and i dont know why i never tried this yet. i dont remember why u zip tied in the first plac. didnt u have a surge/stumble problem as well? anything else youve done i should pay attention to? since i see we have the exact same jeep.... i will try to get around to it this weekend and will post back...

Mine started with a (unknown to me) heat related problem in the PCM. Before it was over i had replaced a lot of sensors and relays, AND wore my PCM connectors out.

It would not idle from a cold start all the way thru warm up without dieing once after idling for about 5 five minutes. It would always crank back up immediately, then going up the road at cruise, it would jump like the engine shut off and back on for a second. After the engine compartment got saturated with heat, it was okay. No codes

I finally discovered (after countless hours with meter, diagrams, ranting on Jeep forum, new sensors, etc) that I could tap on the PCM with a small wrench and it would go dead, unless it was saturated with heat.

I finally convinced my self it was the PCM rather than the connectors when the emiisions monitors on the scanner kept resetting, like i had disconnected the battery. I ran wires from the PCM to a meter on the dash to determine i wasnt loosing voltage.

After a failed repair and return experience, a junkyard PCM that lasted 5 months, and a reman PCM from A1 Cardone (plus the mongo zip ties). She's been purring like a kitten every day for my 80 mile commute.

One thing to pay attention to are the ASD and Fuel pump relays. I've had some no crap problems with those due to the bad PCM furnishing a partial ground . Also the connections to the coil and cam sensor. I had to zip tie those also. You'll get codes to lead you to the coil, cam sensor, and ASD, but the FP relay won't code, it will cause it to stumble if the contacts are weak.

[edit] I discovered the plug issue with the second PCM, gray plug

HTH

 

[ZeeJay1997]

Zeejay... that is the cleanest ZJ engine compartment I have ever seen.

Ya, it's an off road virgin... commuter... poor thing. Engine compartment never been cleaned

 

[JensGCherokee]

Zeejay,

Reading up on what you have wrote, it sounds like what kind of issue I am having right now.. Without the stalling issue. It does feel like it is going to when sitting at a light. When I drop it into neutral though, it subsides, but doesnt completely go away. Now, mine is a 95 I6, completely stock powertrain. It will run fine until it warms up, or if you shut it off after only a min of driving to the store & start it back up, it will start to stumble. Almost like a dead miss. All the symptoms you describe though, are exactly the same. When at 50, when it misses, it almost sounds/feels like the motor is going to fall out the bottom on the thing. I replaced the cap, rotor, plugs, wires, cam/pick-up & crank sensor, fuel pump, fuel filter since it happened. The catalytic converter & o2 sensor was replaced 2 years ago. It's throwing no codes at all & every mechanic I take it to is mind-boggled.

Any ideas? I cant afford no more mechanics saying "i can figure it out" and charge me $90 only to say "It's got me stumped. I'd get rid of it. Sorry, good luck."
Thanks in advance!

 

[purplecty]

IAC, TPS? u check those yet?

 

[ZeeJay1997]

JensGCherokee, What you're describing doesn't sound a lot like the problem I had.

ZJs have many things that can make them stumble and are very sensitive to variations in voltages. The ECU keeps just enough fuel going to the engine to keep it running based on the inputs from the vehicle.

One of the key things to figure out what may be going on is to watch all the gauges. Do tach and speedo react? Does battery meter and fuel gauge move? Do any of the instrument warning lamps flash for a split second? If any of this is going on, the ECU or its supply voltage is suspect.

All connectors and connections under the hood are always suspect, especially the ones on the passenger side. Take all main cables loose and clean both ends, plus the battery posts. The ground on the fender is important too. Plus there are two grounding points on the block, and the case ground for the generator. Pull all fuses and relays under the hood and clean the posts with scotchbright or a small file. If any of the posts are discolored, replace them.

If you know how to use a multimeter and have a wiring diagram, you can spend hours checking different circuits. A scanner will also eliminate many things, and maybe lead you to the problem. There is a lot of info online about OBD2 so you can teach yourself if you have the time. I have ran a lot of miles with my scanner connected. In my opinion, if your going to own a ZJ, these are necessary unless you enjoy feeding money to mechanics for hours of troubleshooting. Time and patience essential and it helps to have something else to drive.

 

[JensGCherokee]

IAC, TPS? u check those yet?

Yes, those have been eliminated as suspects. The one garage replaced it & it still didnt fix the issue, so he did the IAC as well.. Still nothing, so he removed them & put the old ones back in. No big deal to me. It wasnt the issue.

Zeejay,

The oil gauge drops from around 35-40 to like 5 below for a split second. The Tac on the other hand, it depends on the speed im going on how much it drops. But again, for only a split second. No lights flashing.. Although, my ABS light came on after I replaced my fuel pump. Now, when I drove it in today (taking back roads into work) I paid alittle more attention to what it does when I drop it into neutral when at a stop. It doesnt have a miss, but more of a rough idle while stropped. So, while I was coming up to a light (just turned red) I dropped it into neutral while still rolling (5mph & trans was in first) to see if it would help. It did! less of a miss after for a bit, then it would come right back as I started driving. But didnt do anything while leaving the light. I did drive it once with the AC on & it didnt miss as much as with the AC off.. I may have to take a video of it & put up link, cause it misses every 3 seconds while starting out, and every 8 seconds while at a set speed.

 

[ZeeJay1997]

The oil gauge drops from around 35-40 to like 5 below for a split second.

That's a new one on me. Never heard of oil gauge associated with stumble. Not sure how it works on a 95, but on a 97, the oil pressure sending unit feeds the PCM, PCM feeds the instrument cluster on the CCD bus. In the mean while, the BCM monitors the PCM output and turns on the low oil pressure light if the pressure goes too low.

The Tac on the other hand, it depends on the speed im going on how much it drops. But again, for only a split second.

Does the tach seem to follow what the engine is doing, or does it go rogue?

 

[JensGCherokee]

That's a new one on me. Never heard of oil gauge associated with stumble. Not sure how it works on a 95, but on a 97, the oil pressure sending unit feeds the PCM, PCM feeds the instrument cluster on the CCD bus. In the mean while, the BCM monitors the PCM output and turns on the low oil pressure light if the pressure goes too low.

Does the tach seem to follow what the engine is doing, or does it go rogue?

It goes with what the motor is doing.. Same with the oil gauge. I checked the oil level which is good, and also ran another oil pressure gauge (temp) & it didnt agree with the one on the cluster. The Tach on the other hand, reads exactly (+/- maybe a few RPM) of a temp gauge.

 

[ZeeJay1997]

It goes with what the motor is doing.. Same with the oil gauge. I checked the oil level which is good, and also ran another oil pressure gauge (temp) & it didnt agree with the one on the cluster. The Tach on the other hand, reads exactly (+/- maybe a few RPM) of a temp gauge.

This could be indicative of a bad ground or shorting across circuits within the ECM. Have you tried tapping the ECM and wiggling connector?

 

[Canyon411]

.... It sounds like this "stumble/surge" issue is quite common to grand cherokee's. I have been dealing with the same issue on my 95zj and I was tempted to replace alot of the usual suspects such as the idle air control or throttle position sensor. I even considered coil, plug wires, etc. The thing that bugged me the most about the stumble/surge issue was that it was never consistant. I would go three months and never have an issue and then it would start again.

Generally when a sensor goes bad, it creates a consistant problem, not an intermidant one. That is why I have held off replacing the above components and kept looking for a possible cause that would support the intermidant nature of the problem, and the underhood environment where the pcm lives is constantly bombarded with temperature changes, moisture fluctuations, and viberation. It all kinda makes sense so the next opportunity I have, I will be pulling the coolant recovery tank and unplugging the wiring harness connectors to the pcm for inspection of corrosion and loose pins/black marks from shorting or loose connection. A good cleaning with contact cleaner and some fresh dielectric grease hopefully will excersize the stumble deamons from my zj :highfive:

 

[JensGCherokee]

This could be indicative of a bad ground or shorting across circuits within the ECM. Have you tried tapping the ECM and wiggling connector?

I have not tried that yet. I will be doing that tonight. Wiggiling it at first.. I am dropping my daughter off at my fathers for the night, so the short 15 min drive there hopefully will turn over a stone, if not.. Un-plug it & clean everything, refresh the dielectric greese, & see how it runs tomorrow when I pick her up.

 

[ZeeJay1997]

I have not tried that yet. I will be doing that tonight. Wiggiling it at first.. I am dropping my daughter off at my fathers for the night, so the short 15 min drive there hopefully will turn over a stone, if not.. Un-plug it & clean everything, refresh the dielectric greese, & see how it runs tomorrow when I pick her up.

If it runs good for 3 warm up cool-down cycles, then starts acting up again, start hunting an ECM. :thumbsup: